1. Field of the Invention
The present invention relates to a method for printing a functional pattern using a printing apparatus, the printing apparatus applying a recording material on a substrate.
2. Description of Background Art
A printing apparatus may be used to print a functional pattern of recording material on a substrate. Such recording material may be a fluid like ink, a substance like toner or another kind of material like metal or silicon. In case of an inkjet apparatus, drops of recording material are ejected by a plurality of printing elements of a print head of the inkjet apparatus on a substrate. The functional pattern of recording material may form an image of pixels, each pixel comprising at least one ink dot. Such an image may form a mask for producing an electrical device. Even a three-dimensional image may be printed. Electronic devices such as solar cells, printed circuit boards and OLED lighting devices are considered.
The print head and the substrate may be moved relative to one another in at least one direction, for example a main scanning direction or a main scanning direction in combination with a sub-scanning direction, in such a manner that a location on the substrate determined for a dot of the image according to the digital data is exposed to at least one printing element of the print head.
In some industrial applications, at first a patterned conductive layer is printed, which is intended to be etched afterwards. This process is also known as etching. For example, direct printing of an electrical circuit on a substrate to achieve a printed circuit board may be established via etching.
In some other industrial applications, at first a mask is printed by an inkjet apparatus on a substrate, which serves as a base for an electrical device. Gaps in the mask are filled with a conducting material in order to form electrical circuits of the electrical device. After the gaps are filled, the mask is removed from the substrate. This process is also known as plating. For example, printing a negative mask on a substrate for a solar cell allows for a plating process to create conductive electrodes on those parts of a wafer where no ink was printed.
An inkjet apparatus may occasionally have failing nozzles. A nozzle is a printing element of a print head from which an ink drop is ejected on the substrate. Usually, a nozzle ejects ink on a line on the substrate when the print head is moving over it.
Missing drops of recording material resulting in a missing line, due to a failing nozzle may result in unwanted creation of isolated parts of the electrical device. When the printing of the conductive recording material is intended to form a conductive layer for an electrical device, a failing nozzle may isolate a part of the conducting layer. For example, when producing a ground layer for a printed circuit board, a large area is concealed by means of the mask. If a failing nozzle results in an open line in the middle of the mask, this open line will become a fracture line inside the ground layer after etching. This ground layer does not function well since one part of the ground layer remains floating, when the other part is electrically connected to the ground. Such a malfunctioning ground layer may occur when producing an electronic device like a solar cell, a printed circuit board as well as an OLED lighting device.
Missing drops of recording material resulting in a missing line in a mask for an electrical device due to a failing nozzle may create unwanted conductive parts of the electrical device. For example, on the surface of a solar cell this results in a slightly lower efficiency of the finished solar cell, which is no problem.
However, a missing line on an edge of the solar cell may result in a formation of a conductive track from a front side of the solar cell to a backside of the solar cell, resulting in a non-functioning solar cell. An electrically insulated edge is a critical part of the solar cell with regard to current shortage or leakage. A part of an electrical device that is located between two sections of the electronic device, which have to remain electrically separated, may also be a critical part. Such a destructive conducting path between two sections is also known as a short.
When a missing line is detected, the print head is moved to a cleaning unit according to the background art in order to clean the nozzle, which is responsible for the missing line. Such a cleaning will cost productivity due to the extra cleaning time. Also, additional printing swathes have to be made, which lowers an end product throughput and machine productivity. In case of a one pass print strategy, detection of a missing line in a printing process may be too late to correct already printed parts of the mask. Only parts to be printed after the cleaning action will be corrected.